This invention relates to a method of operating a spark-ignition, four-stroke internal combustion engine. More particularly, this invention relates to a method of operating a spark-ignition, four-stroke internal combustion engine wherein the valve train area of the engine and the crankcase section are separated from each other and are lubricated separately.
A problem associated with conventional spark-ignition four-stroke internal combustion engines equipped with exhaust gas aftertreatment devices (e.g., catalytic converters, particulate traps, etc.) is that the lubricating oils for such engines are used in both the crankcase as well as in high wear areas such as the valve train. Because these oils are used in high wear areas they usually contain extreme pressure (EP) agents, which typically contain metal and phosphorus, in order to be effective. During the operation of the engine these EP agents decompose and the resulting decomposition products eventually enter the aftertreatment device resulting in damage to the device. The problem therefore is to provide a lubricant system that adequately addresses the antiwear protection needs of the high wear areas of the engine and yet reduces or avoids damage to the exhaust gas aftertreatment device.
Another problem associated with these engines is that blow-by exhaust gases generated in the crankcase of the engine come into contact with the cam shaft used in the valve train system. Blow-by exhaust gases have been found to be a primary factor affecting cam shaft wear. The problem therefore is to provide a method for preventing the blow-by gases from contacting the cam shaft and thereby prevent excessive wear of the cam shaft.
Another problem associated with the use of conventional spark-ignition four-stroke engines is that oil change intervals lag behind other service intervals. Oil changes are viewed as one of the most aggravating and, in some cases, most costly maintenance aspects of vehicle ownership. Traditionally, intervals have been extended by base stock and additive upgrades. Since the 1920s, for example, the extension has been 15xc3x97 or greater, depending on what is considered the current drain interval. Regardless of this progress, improvements in oil change maintenance have consistently lagged other service intervals such as air filters, brake replacement, and coolant changes. The problem therefore is to improve the lubricant technology for these engines so that the required time interval between oil changes can be increased.
The present invention provides a solution to each of these problems. With the present invention lubricating oil compositions characterized by a low-level amount of or the absence of harmful EP agents are used in the crankcase section of the engine and therefore the exhaust gas aftertreatment device is protected from harmful exposure to such agents. Also, because the cam shaft of the engine is separated from the crankcase section of the engine, harmful blow-by exhaust gases generated in the crankcase do not come into contact with the cam shaft and therefore do not cause wear in the cam shaft. In accordance with one embodiment of the invention, the oil change intervals for these engines are extended due to the fact that used crankcase oil is continuously or periodically removed from the crankcase and replaced with new oil.
U.S. Pat. No. 4,392,463 discloses a diesel engine having a first lubrication system, containing conventional engine oil, used to lubricate that section of the engine subjected to excessive wear-the valve train including the cam shaft, valve lifters, rocker arm, valve stems, etc., and a second lubricant system, utilizing diesel fuel, for lubricating the remaining section of the engine-the crankshaft and associated parts, pistons, connecting rods, etc. By being exposed to crankcase blowby exhaust gases, diesel fuel used to lubricate the crankshaft, etc. absorbs pollutants and contaminants contained therein and recirculates these contaminants through the fuel system to be burned and exhausted. By constantly being lubricated with fresh lubricant, wear on these specific parts is reduced. The reference indicates that frequent lubrication changes have been eliminated because the diesel fuel/lubricant is continuously changed and circulated through the fuel system. Since the engine oil and the first lubrication system is not exposed to crankcase blowby exhausted gases, its useful life is prolonged, thus reducing the frequency of required oil changes.
This invention relates to a method of operating a spark ignition four-stroke internal combustion engine comprised of a valve train and a crankcase and equipped with an exhaust gas aftertreatment device, said method comprising:
(A) operating said engine using a gasoline fuel composition, the exhaust gas from the operation of said engine being advanced through said aftertreatment device;
(B) lubricating said crankcase using a first lubricating oil composition, said first lubricating oil composition optionally containing an extreme-pressure additive comprised of metal and phosphorus, provided the amount of phosphorus contributed to said first lubricating oil composition by said extreme-pressure additive does not exceed about 0.04% by weight based on the weight of said first lubricating oil composition; and
(C) lubricating said valve train using a second lubricating oil composition.
In one embodiment, the inventive method further comprises the following additional steps:
(D) removing part of said first lubricating oil composition from said crankcase, said removed part of said first lubricating oil composition (i) being combined with said gasoline fuel composition and consumed with said gasoline fuel composition as said engine is operated or (ii) being combined with the exhaust gas from said engine and removed from said engine with said exhaust gas, said first lubricating oil composition in this embodiment being characterized by the absence of extreme pressure additives comprised of metal and phosphorus; and
(E) adding an additional amount of said first lubricating oil composition to said crankcase to replace said removed part of said first lubricating oil composition.